1. Field of the Invention
This invention relates generally to using z-pins in composite laminates and relates specifically to using z-pins to conduct heat through the thickness of composite laminates.
2. Description of the Prior Art
Z-pinning is used to reinforce composite joints, wherein carbon fiber composite pins are inserted through a composite laminate. An instrument uses ultrasonic energy and pressure to force the z-pins through the laminate. Z-pins available for reinforcing structural joints are typically made with standard modulus T-300 carbon fiber. However, this carbon fiber has fairly low thermal conductivity.
There are many systems on an advanced fighter aircraft which have thermal management issues. Typically a heat exchanger is used to cool electronic weapon systems, but heat exchangers can be large, complicated pieces of equipment which are difficult to install because of wiring and plumbing concerns. Prior art methods of disposing of excess heat include, for example, transferring heat into fuel in a wing structure. Though effective, these heat exchanger units are also expensive, take up valuable space in an aircraft, and require maintenance.
Material scientists are exploring new materials capable of passive thermal management. This special class of materials improves the efficiency of current heat exchangers, but can also be designed to direct heat to a desired location. Many of these new materials have a combination of deficits, such as low stiffness, poor toughness, very high cost and difficulties in manufacturing airframe components.
In U.S. Pat. No. 5,542,471, Dickinson describes a xe2x80x9cHeat Transfer Element Having Thermally Conductive Fibers,xe2x80x9d which is a solid structure capable of transferring heat. This patent describes a composite structure comprising fiber bundles oriented to conduct heat through the thickness of the structure, the entire structure behaving as a heat exchanger. However, the Dickinson structures must be used when creating parts in order to allow the heat transfer, but these structures may not provide the required characteristics for particular components or applications.
Therefore, there is a need for a modification of typical structural composites to allow for greater heat transfer through the thickness of the composites.
This invention disclosure describes a composite structure which increases the thermal conductivity through the thickness. The invention would also allow current structural composites to be modified to behave as a heat path. For example, the composite skin of an air inlet could be readily modified to also behave as a heat exchanger, allowing heat to be dumped into air entering the aircraft engine. This design might create the option of altering the infrared signature of the aircraft by preferentially moving heat to a desired location for disposal.
An apparatus is provided for transferring heat through the thickness of aircraft structure formed from composite laminates. Z-pins having a high thermal conductivity are inserted through the composite laminate and placed in thermal communications with a heat source at the end of each z-pin on one side of the structure. The ends of the z-pins on the opposite side of the structure as the heat source are in thermal communication with a heat sink. Each of the heat source and heat sink may be a fluid, which carries heat to or away from the z-pins by convective currents, or a component that is mechanically connected to the z-pins, which conduct heat from or to the component.